Multi-stage apparatus for installing tubular goods

ABSTRACT

A pipe gripping assembly includes, among other components, a fluid conducting swivel, a fluid-powered linear actuator and a pipe gripping assembly. The linear actuator has a central rod mounted within a multi-stage, segmented barrel assembly. Each barrel segment acts as a piston, with control fluid forces being transmitted to the barrel assembly to selectively extend or retract the barrel assembly in order to engage or disengage the pipe gripping assembly. By aggregating such force, the total combined force generated by the barrel piston assemblies, the actuator assembly of the present invention can operate using pneumatic control fluid, and can operate at much lower control fluid pressures than other actuators.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to an apparatus for conveying pipe and other tubular goods within wellbores penetrating subterranean formations. More particularly, the present invention pertains to a fluid powered, multi-stage linear actuator and associated equipment that can be used in many different applications including, without limitation, in connection with casing running tools.

2. Brief Description of the Prior Art

Oil and gas operations frequently involve the use of pipe and/or other tubular goods manipulated from a surface drilling rig or other surface facility. Such tubular goods are usually inserted into a well in a number of separate sections of substantially equal length called “joints.” Such joints are typically screwed together or otherwise joined end-to-end at the rig floor of a drilling rig in order to form a substantially continuous “string” of pipe that reaches downward into the earth's crust. As the bottom or distal end of the pipe string extends further into a well, additional sections of pipe are added to the upper end of the pipe string at said drilling rig.

After a well has been drilled to a desired depth, a relatively large diameter and heavy string of pipe—commonly referred to as “casing”—is inserted into the drilled hole and cemented in place. Cement slurry is pumped down the central pipe bore, circulated into the annular space between the exterior surface of the pipe and the inner surface of the wellbore, and permitted to harden. In addition to other benefits, such casing provides structural integrity to a wellbore, and isolates subterranean horizons penetrated by said wellbore from one another.

Conventional casing installation operations typically involve specialized crews and equipment transported to a well site for the sole purpose of installing casing into a well. During such conventional casing installation operations, powered casing tongs, pipe gripping casing elevators and spider slips, dedicated hydraulic power unit(s) and other ancillary components must typically be mobilized to a well location and set up immediately prior to the casing installation operation. Specialized casing crews must rig up and operate the equipment, connect the joints of casing to run in the well, and demobilize the equipment following completion of the casing installation job.

Drilling rig top drive systems can be used to pick up sections of pipe, connect such pipe sections together, and provide the torque necessary to drill wells. Although such top drive units have been used on drilling rigs for some time to make-up drill pipe connections and to efficiently drill wells, such top drive systems generally have not been used to make-up and run casing strings until relatively recently.

Such top drive systems are typically used together with running tools (RT) in order to install casing within wellbores. In many cases, casing can be run more efficiently and for less cost than with conventional casing crews and equipment. Because top drive systems can be used to provide torque to make up casing connections, specialized casing tongs are frequently not required with RT's. Further, fewer personnel are needed on and around the rig floor during the casing running operations, resulting in faster and more efficient casing installation. Full mechanization of casing installation activities on the drilling floor is not always possible but every effort to limit the contact between the more dangerous activities and people is beneficial and worthwhile.

In most cases, a RT is connected immediately below a rig's top drive unit prior to commencement of casing installation operations. A single-joint elevator, supported by a RT, is typically used to lift individual joints of casing from a V-door or pipe rack to a well. In this manner, each joint of casing is stabbed and threadedly connected to a pipe string already installed in a well. The top drive and attached RT are lowered until the RT extends past the top of the new joint being added. The slips of the RT are set on the new joint of casing, and the top drive is used to apply required torque (through the RT) to make up the threaded connection of the casing. The connected casing string can then be lowered into the wellbore using the top drive unit. Importantly, the casing string can be rotated and/or reciprocated during this step to facilitate installation of the casing in the wellbore.

In addition to permitting rotating and reciprocating of casing and other pipe, RT's typically permit reaming and drilling with casing. Such reaming and drilling with casing requires a casing RT that can operate at higher RPM's than conventional RT's or other casing running equipment, and could require rotation for many hours before stopping to pick up another joint of casing.

Efficiency in connection with oil and gas operations, especially in terms of drilling rate, has been addressed with great earnest for many years. Pipe string assembly rate typically has about the same cost-effect as drilling rate. The present invention addresses an increase in efficiency of such pipe string assembly operations (and a resulting decrease in costs associated with such operations), and does so without sacrificing safety concerns.

Conventional RT devices are often severely limited in terms of lifting capacity or rotating speed, or both. Thus, there is a need for an RT assembly having a linear actuator that can support and lift heavy axial loads, while permitting high speed pipe rotation. The RT assembly should be capable of being pneumatically operated.

SUMMARY OF THE INVENTION

The present invention comprises a pipe gripping apparatus that includes, among other components, a fluid conducting swivel and a fluid powered linear actuator. Said linear actuator has a central rod member which acts as a primary load path used to lift, rotate and apply torque to a casing string or other pipe string. The upper portion of said rod can connect to a quill of a rig's top drive unit, while the lower portion of said rod can be connected to a pipe gripping slip assembly.

Generally, the linear actuator of the present invention comprises a rod concentrically disposed within a barrel assembly that can be selectively extended or retracted. Said actuator has a cap end fixed to said rod at or near the upper end of said actuator, and a movable end that is attached to said barrel assembly. In a preferred embodiment, said barrel assembly comprises a plurality of cooperating barrel segments, each of which is connected to another segment by means of a split load ring.

Each load ring has a plurality of teeth that corresponds to mating teeth that are formed (typically machined) onto the outer surface of the barrel segment ends. Said load rings not only hold said barrel segments together, but also to act as a retainer for barrel pistons movably disposed within said barrel assembly. Each barrel segment acts as an individual piston with forces being transmitted to the barrel assembly; because such forces are aggregated, the total combined force generated by said barrel piston assemblies are greater at the lower (movable) end of the barrel assembly.

Said piston assemblies are segregated from each other by sealed dividers that are each held in fixed placement at desired positions along the length of said actuator rod. The combination of said movable barrel piston assemblies on the barrel, and the fixed dividers on the rod, causes the actuator assembly to act as a tandem cylinder. Fluid pressure is selectively provided to individual cylinder segments through ported stabilizer rods that feed “extend” or “retract” sides in unison; said stabilizer rods serve as both structural stabilizers, as well as fluid conduits.

In a preferred embodiment, fluid to control said linear actuator is introduced through a swivel assembly. Although other swivel assemblies can be employed without departing from the scope of the present invention, said fluid swivel assembly is disclosed in pending patent application Publication No. US2014/0060853, which is incorporated herein by reference for all purposes. In a preferred embodiment, said swivel assembly has an outer housing, an inner hub rotatably disposed within said housing, and fluid pressure seals. Said seals only contact the inner hub when fluid pressure is introduced; with no fluid pressure applied between said housing and hub, said hub is free to rotate with only bearing friction resisting such rotation. As a result, the RT of the present invention has only swivel bearing speed limitations as its upper rotational speed limit.

Once said control fluid flows through said swivel assembly, said fluid is directed to a pair of positive sealing check valves leading to said actuator assembly of said RT, one for checking while extending (setting pipe gripping slips), and the other for checking while retracting (releasing pipe gripping slips). Said check valves allow for applied fluid pressure to be selectively removed prior to rotation, while still providing the required force to operate and control the actuator of the RT. A first stage of the RT actuator can have an extended volume area to act as a receiver for energy storage.

Said control fluid enters the multi-stage linear actuator of the present invention. As a result of the multi-stage design, said actuator of the present invention can operate using much lower control fluid pressures than conventional RT devices. Normally, control fluid pressures in the range of 1,500 to 3,000 psi or more are required in order to actuate a RT's pipe gripping slips. For that reason, conventional RT's are typically, if not exclusively, operated using hydraulic oil or other liquid control fluid that permit such higher operating pressures; it has generally not been feasible to operate a conventional casing RT using pneumatic pressure alone for purposes of actuating pipe gripping slips and applying torque for pipe thread connection operations.

Because the RT of the present invention is capable of operating using pneumatic power, the present invention does not require a hydraulic power source in order to operate. Rather, the power source for the RT of the present invention can be a drilling rig's existing air supply (which typically operates at much lower pressures), which significantly reduces cost and logistical challenges associated with transporting the present invention to and from a well site, particularly at offshore or remote locations. Alternatively, pneumatic air pressure can be provided from a compressor including, without limitation, a stand-alone air compressor.

Notwithstanding the foregoing, the actuator of the present invention can be alternatively configured for operation using hydraulic control fluid. Such alternative configuration can serve a great advantage for certain applications such as, for example, small land rigs or slant rigs where limited space is available. In this alternative configuration, the outside diameter of the actuator assembly can be greatly reduced (for example, in certain applications 10 inches or less) without sacrificing lifting capacity, thereby making use on small rigs much safer for rig personnel.

BRIEF DESCRIPTION OF DRAWINGS/FIGURES

The foregoing summary, as well as any detailed description of the preferred embodiments, is better understood when read in conjunction with the drawings and figures contained herein. For the purpose of illustrating the invention, the drawings and figures show certain preferred embodiments. It is understood, however, that the invention is not limited to the specific methods and devices disclosed in such drawings or figures.

FIG. 1 depicts side view of a RT equipped with the apparatus of the present invention.

FIG. 1A depicts side view of a RT equipped with the apparatus of the present invention.

FIG. 2 depicts a side sectional view of the multistage actuator assembly of the present invention.

FIG. 3 depicts a side sectional segment of the present invention showing the arrangement of the barrel piston assembly, fixed divider assembly, ported tie rods, central rod, and axially joined barrel segments.

FIG. 4 depicts a side sectional view of a barrel piston assembly of the present invention.

FIG. 4 a depicts a top perspective view of barrel piston assembly of the present invention.

FIG. 5 depicts a side view of a barrel load ring of the present invention.

FIG. 5 a depicts a detailed view of a portion of barrel load ring depicted in FIG. 5 and, in particular, barrel load teeth and piston load lug.

FIG. 6 depicts a side sectional view of central rod, and a fixed divider assembly attached to said rod with split load rings.

FIG. 7 depicts a side partial exploded view of a portion of central rod segment with split load rings and capture ring.

FIG. 8 depicts a side perspective view of a multi-stage cylinder assembly of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 depicts side view of a RT assembly 10 equipped with the pipe gripping assembly of the present invention, while FIG. 1 a depicts side view of a RT assembly 10 equipped with the pipe gripping assembly of the present invention. Generally, RT assembly 10 comprises fluid swivel assembly 30, linear actuator assembly 20, pipe gripping slip assembly 40 and fluid fill-up assembly 50. Single joint elevators 11 are attached to said RT assembly 10 beneath said fluid fill-up assembly 50.

As depicted in FIG. 1, fluid swivel assembly 30 can be installed below a top drive unit of a drilling rig to allow for remote powering of tools or equipment (such as RT assembly 10) situated below said top drive unit. In this regard, swivel assembly 30 is generally used to supply control fluid (such as pressurized hydraulic or pneumatic fluid) through said fluid swivel assembly 30 in order to actuate tools or equipment situated below said swivel assembly (including, without limitation, linear actuator assembly 20), while permitting rotation of such tools or equipment below said swivel assembly.

Control fluid passing through said fluid swivel assembly 30 provides power to linear actuator assembly 20 which, in turn, is used to actuate pipe gripping assembly 40. During pipe installation operations, fluid fill-up tool 50 can be partially received within the upper end of a said pipe section suspended from RT assembly 10. Said fluid fill-up tool 50, which operates in a manner well known to those having skill in the art, allows for filling of suspended pipe sections with drilling mud or other fluid during casing installation operations.

FIG. 2 depicts a side sectional view of multistage linear actuator assembly 20 of the present invention, as well as fluid swivel assembly 30. Said linear actuator assembly 20 comprises central rod 200 which acts as a primary load member used to lift, support, rotate and apply torque to a casing string or other pipe string supported by said central rod 200. Upper portion 210 of said rod 200 can connect, typically via threaded cross over sub 230, to a quill or other output of a rig's top drive unit (not depicted in FIG. 2), while lower portion 220 of said rod 200 can connect to a pipe gripping slip assembly (such as pipe gripping assembly 40, depicted in FIGS. 1 and 1 a), which can be used to grip a casing string or other pipe section(s).

Still referring to FIG. 2, linear actuator assembly 20 has upper barrel cap end member 240 fixedly attached to said rod 200, while base member 250 is movably disposed along the length of rod 200. In a preferred embodiment, said base member 250 has central through bore 251; rod member 200 is slidably disposed through said central through bore 251. At least one seal member 252 is disposed between the inner surface of said bore 251 and the outer surface of rod 200, and provides a fluid pressure seal between said surfaces. Said at least one seal member 252 can comprise sealing element(s) constructed of rubber, elastomeric material or other sealing material well known to those having skill in the art. Attachment hub 253 having apertures 254 is attached to base member 250.

Base member 250 is connected to a lowermost barrel segment 502, as well as outer barrel cover 506. A plurality of substantially axially aligned barrel segments 502 are joined by barrel load rings 504. At least one seal member 241 is disposed between the inner surface of uppermost barrel segment 502 and the outer surface of upper cap member 240, and provides a fluid pressure seal between said surfaces. Said at least one seal member 241 can comprise sealing element(s) constructed of rubber, elastomeric material or other sealing material well known to those having skill in the art.

An annular space is defined between the outer surface of rod 200 and the inner surface of joined barrel segments 502. Ported tie rods 600, each having central through bore 601, are attached to said barrel upper cap member 240, and extend within said annular space in substantially parallel orientation with central rod 200. A plurality of barrel piston assemblies 300, each of said barrel piston assemblies 300 having a central through bore, are slidably disposed along the outer surface of ported tie rods 600. Said barrel piston assemblies 300, in conjunction with barrel load rings 504, are attached to interconnected barrel segments 502.

Fixed divider assemblies 400 are anchored at desired positions along the length of rod 200 and divide said annular space (that is, the space between the outer surface of rod 200 and the inner surface of joined barrel segments 502) into a plurality of separate segments or chambers. Said fixed divider assemblies 400 form a fluid pressure seal against the outer surface of said rod 200 and the inner surfaces of barrel segments 502. Barrel piston assemblies 300 (connected to joined barrel segments 502) are capable of moving axially between said anchored divider assemblies 400 within the annular space formed between the outer surface of rod 200 and the inner surface of joined barrel segments 502.

It is to be observed that axial movement of said barrel piston assemblies 300 within said annular space results in extension or retraction of the outer barrel assembly of linear actuator assembly 20, depending upon the direction of travel of said barrel piston assemblies 300. As said barrel piston assemblies 300 move upward within said annular space, base member 250, interconnected barrel segments 502 and barrel load rings 504 also move upward (that is, generally toward fluid swivel assembly 30), causing axial retraction of actuator assembly 20. Conversely, as said barrel piston assemblies 300 move downward within said annular space, base member 250, interconnected barrel segments 502 and barrel load rings 504 also move downward (that is, generally away from fluid swivel assembly 30), thereby resulting in axial extension of actuator assembly 20

FIG. 3 depicts a detailed side sectional view of a portion of actuator assembly 20 of present invention. Central rod 200, which acts as a primary load member used to lift, support, rotate and apply torque to a casing string or other pipe string supported by said central rod 200, has central through bore 201. Axially aligned barrel segments 502 are threadedly joined to interconnecting barrel load rings 504 to form a barrel assembly around central rod 200, and define an annular space between the outer surface of rod 200 and the inner surfaces of said interconnected barrel segments 502 and load rings 504. Ported tie rods 600, each having central through bore 601, extend within said annular space and are oriented substantially parallel to said rod 200.

Fixed divider assemblies 400 are disposed within the annular space between the outer surface of rod 200 and the inner surface of joined barrel segments 502, and divide said annular space into a plurality of separate segments or chambers along the length of rod 200. Said fixed divider assemblies 400, which are anchored in position along the length of rod 200, further comprise piston seals 401 and glyd rings 402 that permit barrel segment 502 to move axially while maintaining a dynamic fluid pressure seal against said fixed divider assemblies 400.

Specifically, fixed divider assemblies 400 are each anchored in position along the length of rod 200 using teeth 203 and split load rings 405, capture ring 406 and retaining ring 407. Each divider assembly 400 is also fluid pressure sealed against the outer surface of central rod 200 with at least one O-ring 410, while ported tie rods 600 are fluid pressure sealed using O-ring 403. Divider assemblies 400 have either directional port 408 or 409, opposite said O-rings 403, depending upon whether said port is designed for extension or retraction as discussed below.

A plurality of barrel piston assemblies 300, each of said barrel piston assemblies 300 having a central through bore 320, are slidably disposed along the outer surface of said ported tie rods 600. Said barrel piston assemblies 300, in conjunction with barrel load rings 504, interconnect barrel segments 502. Barrel piston assemblies 300 (connected to joined barrel segments 502) are capable of moving axially between said anchored divider assemblies 400 within the annular space formed between the outer surface of rod 200 and the inner surface of joined barrel segments 502.

Still referring to FIG. 3, barrel seal assembly 300 comprises barrel seals (typically O-rings) 301, main rod seal carrier 311 and tie rod seal carrier 312. Central lug 310 provides a load shoulder for main seal carrier 311. Main rod seal carrier 311 has rod seal 304 and glyd seal ring 305 for creating a fluid pressure seal against the outer surface of main rod 200. Retaining ring 307 is used to secure main rod seal carrier 311 in place.

Similarly, tie rod seal carriers 312 have rod seals 302 and glyd seal ring 303 for creating a fluid pressure seal against the outer surface of a tie rod 600, as well as outer O-ring 309. Retaining ring 306 is used to secure main rod seal carrier 312 in place. Load shoulder recess 313 provides a load shoulder for receiving a mating load lug of a barrel load ring 504.

FIG. 4 depicts a side sectional view of a barrel piston assembly 300 of the present invention, while FIG. 4 a depicts an overhead perspective view of said barrel piston assembly 300 of the present invention. Referring to FIG. 3 and FIG. 4 a, barrel piston assembly 300 generally comprises ring like body member 330 having central through bore 320 extending through said body member 330. A plurality of ancillary through bores 325 also extend through said body member 330; in a preferred embodiment, said ancillary through bores 325 are disposed substantially around said central through bore 320 and are oriented substantially parallel to central through bore 320.

Referring to FIGS. 3 and 4, in a preferred embodiment barrel seal assembly 300 comprises removable main rod seal carrier 311 and tie rod seal carrier 312 removeably disposed within body 330. Central lug 310 extends around central through bore 320 and provides a load shoulder for main seal carrier 311. Said seal carriers 311 and 312 can be easily removed and replaced in the event of excessive wear on pressure seal members or failure of said seal members. Main rod seal carrier 311 has rod seal 304 and glyd seal ring 305 for creating a fluid pressure seal against the outer surface of main rod 200. Retaining ring 307 is used to secure main rod seal carrier 311 in place within said body member 330.

Similarly, tie rod seal carriers 312 have rod seals 302 and glyd seal ring 302 for creating a fluid pressure seal against the outer surface of a tie rod 600, as well as outer O-ring 309. Retaining ring 307 is used to secure main rod seal carrier 311 in place within said body member 330. Semi-circular extensions 308 are disposed on the upper and bottom surfaces of body 330 to provide stand-off when said barrel seal assembly 300 is in a fully extended or fully retracted position. Load shoulder recess 313 extends around the outer surface of body member 330 and provides a load shoulder for receiving a mating load lug of a barrel load ring 504.

FIG. 5 depicts a side view of a barrel load ring 504 of the present invention, and FIG. 5 a depicts a detailed view of a portion of barrel load ring 504 depicted in FIG. 5 and, in particular, barrel load teeth 507 and piston load lug 505. Said piston load lug 505 can be received within load shoulder recess 313 of barrel piston assembly 300.

FIG. 6 depicts a side sectional view of central rod 200, and fixed divider assembly 400 which can be attached to said rod 200 with split load rings 405. Fixed divider assembly 400 generally comprises piston seal ring 401 for mating with a barrel segment 502 (not shown in FIG. 6). Piston glyd ring is provided for sealing against a barrel segment 502, while static seal O-ring 403 is provided for sealing against a ported tie rod. Said fixed divider assembly 400 also comprises split load ring 405, capture ring 406 and retaining ring 407.

Still referring to FIG. 6, ports 408 and 409 are oriented in opposing axial directions. When actuator assembly 20 is extended, port 408 serves as a flow path for addition of control fluid into said actuator assembly, while opposing port 409 serves as flow path for exhausting/venting of said control fluid (as generally depicted in FIG. 3). Conversely, when actuator assembly 20 is retracted, port 409 serves as a flow path for addition of control fluid into said actuator assembly, while opposing port 408 serves as flow path for exhausting/venting of said control fluid.

FIG. 7 depicts a side partially exploded view of a main rod segment 200 with split load rings 405 and capture ring 406. Split load rings 405 have inner thread-like teeth 409 that mate with thread-like teeth 203 disposed on the outer surface of rod segment 200. Said split load rings 405 can be anchored at desired positions along the length of rod 200. Said rod 200 is disposed within capture ring 406.

FIG. 8 depicts a side perspective view of a multi-stage cylinder assembly of the present invention comprising a plurality of axially aligned ported tie rods 600. Said ported tie rods 600 have a central through bore 601, as well tie rod head 602 that captures tie rod 600 between a swivel base and a cylinder head or barrel cap member (such as barrel cap member 240 depicted in FIG. 2). A plurality of transverse ports 604 extend through tie rods 600, providing fluid communication with central through bore 601.

Referring to FIG. 2, in operation control fluid (typically air) is introduced into ported tie rod 600, causing piston assembly 300 to move axially in a desired direction along central rod 200. Said barrel piston assembly 300 is fluid pressure sealed against central rod 200 in both axial directions via seals 304, and glyd rings 305 mounted in a removable seal carrier 311. Barrel piston assembly 300 also seals ported tie rods 600 with a plurality of rod seal carriers 312; said sealed rod carriers 312 are sealed in both directions with seals 302.

When extending linear actuator assembly 20, control fluid enters through ported tie rod 600 and is directed into staged annular segment(s) through ports 604. Said control fluid is selectively directed though port 409 in divider assembly 400, causing axial movement of barrel piston assemblies 300 which acts to move barrel base member 250 axially downward and extend said actuator barrel. Conversely, when retracting linear actuator assembly 20, control fluid enters through ported tie rod 600 and is selectively directed though ports 408; such control fluid causes upward axial movement of barrel piston assemblies 300, which acts to move barrel base member 250 axially upward and retract said actuator barrel. Exhaust flow of control fluid is directed out of said barrel assembly though opposing port(s) in divider assemblies 400 and tie rods 600 and vented, depending on an extend or retract function, which occurs at all stages of the cylinder simultaneously.

With all barrel piston assemblies 300 moving under fluid pressure, the resultant output force is the piston area×psi×the number of stages. Further, it is to be observed that stages can be added or removed from said linear actuator assembly 20 as desired in order to adjust the axial force generated by said actuator assembly 20, as well as the length of said actuator assembly 20.

Each load ring 405 has a plurality of teeth 507 that corresponds to mating teeth that are formed (typically machined) onto the outside of the barrel segment ends. Said load rings 405 not only hold barrel segments 502 together, but also act as a retainer for barrel piston assemblies 300 that are movably disposed. Each barrel piston assembly 300 acts as an individual piston with forces being transmitted to the barrel member; because such forces are aggregated, the total combined force generated by said barrel piston assemblies are greater at the lower (movable) end of the barrel assembly.

Such piston assemblies 300 are segregated from each other by sealed divider assemblies 400 that are each mechanically held in fixed placement at desired positions along the length of actuator rod 200. The combination of said movable barrel piston assemblies on the barrel, and the fixed dividers on the rod, causes the actuator assembly to act as a tandem cylinder. Fluid pressure is provided to individual cylinder segments through ported stabilizer rods that feed “extend” or “retract” sides in unison; said stabilizer rods serve as both structural stabilizers, as well as fluid conduits. Fixed dividers are sealed and ported in order to direct fluid flow accordingly.

In a preferred embodiment, fluid to control said linear actuator assembly 20 of the present invention is introduced through a swivel assembly. Although other swivel assemblies can be employed without departing from the scope of the present invention, said fluid swivel assemblies comprises the swivel disclosed in pending patent application Publication No. US2014/0060853, which is incorporated herein by reference for all purposes. In a preferred embodiment, said swivel assembly has an outer housing, a hub rotatably disposed within said housing, and fluid pressure seals. Said seals only contact the inner hub when fluid pressure is introduced; with no fluid pressure applied, said hub is free to move with only bearing friction,

Once said control fluid has moved through said swivel assembly, it is directed through a pair of positive sealing check valves leading to said actuator assembly of said RT, one for checking while extending (setting pipe gripping slips), and the other for checking while retracting (releasing pipe gripping slips). Said check valves allow for applied fluid pressure to be selectively removed from said swivel assembly prior to rotation, while still providing the required force to operate and control the actuator of the RT. In a preferred embodiment, a first stage of the RT actuator has an extended volume area to act as a receiver for energy storage.

As a result of its multi-stage design, said actuator assembly 20 of the present invention can operate using much lower control fluid pressures than conventional RT devices. Further, because the RT of the present invention is capable of operating using pneumatic power, actuator assembly 20 of the present invention does not require a hydraulic power source in order to operate. Rather, the power source for the RT of the present invention can be a drilling rig's existing air supply (which typically operates at much lower pressures), which significantly reduces cost and logistical challenges associated with transporting the present invention to and from a well site, particularly at offshore or remote locations. Alternatively, pneumatic air pressure can be provided from a compressor including, without limitation, a stand-alone air compressor.

Notwithstanding the foregoing, the actuator of the present invention can be alternatively configured for operation using hydraulic control fluid. In this alternative configuration, the outside diameter of the actuator could be greatly reduced (for example, in certain applications 10 inches or less).

Referring to FIG. 2, extension of linear actuator 20 of the present invention causes lower base member 250 to move axially relative to central rod member 200. As said lower base member 250 moves toward pipe gripping slip assembly 40, axial force is applied to linkage members 41 connected to attachment hubs 253 and, in turn, to slip members of said pipe gripping slip assembly 40 (see FIG. 1). When said slip members are actuated, a wedging action is formed by a tapered slip bowl and mating tapered slip dies, causing said dies to move against said pipe in order to frictionally grip said pipe in a manner well known to those having skill in the art. Similarly, when said actuator assembly 20 of the present invention is retracted, said slip dies move away from said pipe in order to release such gripping force from said pipe in a manner well known to those having skill in the art.

In the embodiment depicted in FIGS. 1 and 1 a, pipe gripping slip assembly 40 is “external” because it grips against the external or outer surface of gripped pipe; however, it is to be understood that the actuator assembly of the present invention can also be used in connection with internally actuating pipe gripping slip assemblies (that is, pipe slip assemblies that grip against the internal surface of a pipe section).

The above-described invention has a number of particular features that should preferably be employed in combination, although each is useful separately without departure from the scope of the invention. While the preferred embodiment of the present invention is shown and described herein, it will be understood that the invention may be embodied otherwise than herein specifically illustrated or described, and that certain changes in form and arrangement of parts and the specific manner of practicing the invention may be made within the underlying idea or principles of the invention. 

What is claimed:
 1. An apparatus for installing pipe in a wellbore comprising: a) a linear actuator comprising: i) a central tubular member; ii) a barrel assembly disposed around said central tubular member and having an adjustable length; and b) a pipe gripping apparatus adapted to frictionally grip a section of pipe; c) at least one linkage member connecting said barrel assembly to said pipe gripping apparatus.
 2. The apparatus of claim 1, wherein said linear actuator further comprises an annular space between an outer surface of said central tubular member and an inner surface of said barrel assembly.
 3. The apparatus of claim 2, further comprising at least one barrel piston member moveably disposed within said annular space.
 4. The apparatus of claim 3, wherein said at least one barrel piston assembly is connected to said barrel assembly, and axial movement of said at least one barrel piston causes the length of said barrel assembly to change.
 5. The apparatus of claim 1, wherein said linear actuator is pneumatically operated.
 6. A linear actuator comprising: a) a central tubular member having a through bore and an outer surface; b) at least one barrel segment having an inner surface, wherein said at least one barrel segment is disposed around said central tubular member to define an annular space between said outer surface of said tubular member and said inner surface of said barrel segment; c) a plurality of divider members affixed to said outer surface of said central tubular member within said annular space; and d) at least one piston member attached to said at least one barrel segment, and movably disposed within said annular space between said divider members.
 7. The apparatus of claim 6, wherein axial movement of said at least one piston member causes said at least one barrel segment to move axially relative to said central tubular member.
 8. The apparatus of claim 6, further comprising at least one elastomeric seal member between each of said divider members and said at least one barrel segment.
 9. The apparatus of claim 6, further comprising at least one elastomeric seal member between said at least one piston member and said outer surface of said central tubular member.
 10. The apparatus of claim 6, further comprising a plurality of tubular tie rods disposed within said annular space and oriented substantially parallel to said central rod.
 11. The apparatus of claim 10, wherein each of said tie rods have a central through bore and a plurality of transverse bores extending from said central through bore into said annular space.
 12. The apparatus of claim 10, wherein said at least one piston member has a plurality of through bores oriented substantially parallel to the longitudinal axis of said central tubular member, and said tie rods are moveably received within said through bores.
 13. The apparatus of claim 12, further comprising: a) at least one elastomeric seal member between said divider members and said at least one barrel segment; b) at least one elastomeric seal member between said at least one piston member and said outer surface of said central tubular member; and c) at least one elastomeric seal member between said at least one piston member and said tie rods.
 14. The apparatus of claim 6, wherein said linear actuator is pneumatically operated.
 15. A linear actuator comprising: a) a central tubular member having a through bore and an outer surface; b) a barrel cap member fixedly attached to said central tubular member; c) a barrel base member having a central bore, wherein said tubular member is movably received within said central bore; d) at least one substantially cylindrical barrel segment attached to said barrel base member and having an inner surface, wherein said at least one barrel segment is disposed around said central tubular member to define an annular space between said outer surface of said tubular member and said inner surface of said barrel segment; e) a plurality of divider members fixedly attached to said central tubular member within said annular space, wherein said divider members extend substantially from said outer surface of said central tubular member to said inner surface of said at least one barrel segment; and f) at least one piston member attached to said at least one barrel segment, and movably disposed within said annular space between said divider members.
 16. The apparatus of claim 15, wherein axial movement of said at least one piston member causes said barrel base member and said at least one barrel segment to move axially relative to said central tubular member.
 17. The apparatus of claim 15, further comprising at least one elastomeric seal member between each of said divider members and said at least one barrel segment.
 18. The apparatus of claim 15, further comprising: a) at least one elastomeric seal member between said at least one piston member and said outer surface of said central tubular member; and b) at least one elastomeric seal member between said barrel base member and said outer surface of said central tubular member.
 19. The apparatus of claim 15, further comprising a plurality of tubular tie rods disposed within said annular space and oriented substantially parallel to said central rod.
 20. The apparatus of claim 19, wherein each of said tie rods have a central through bore and a plurality of transverse bores extending from said central through bore into said annular space. 